Magnetic guiding device

ABSTRACT

The invention concerns a magnetic guiding device ( 1 ) having at least one element ( 2 ) to be guided magnetically in the axial direction, e.g. a shaft or an actuation member that is movable in the axial direction, the element ( 2 ) having a radial flange ( 14 ) made of magnetizable material that is enclosed by an axial yoke ( 47 ) made of ferromagnetic material and constituting a stator, forming magnet gaps ( 51, 52 ) in which is producible, by means of a combination of permanent magnets and electromagnets ( 53, 54, 55 ), an axial magnetic flux with which the axial position of the element ( 2 ) can be influenced, which is characterized in that in the axial yoke ( 47 ), at least one pair of axially oppositely polarized permanent magnets ( 53, 54 ) are arranged axially next to one another, and an electromagnetic coil ( 55 ) is moreover arranged radially adjacently as an electromagnet, the magnetic flux in the coil ( 55 ) being controllable in such a way that an asymmetrical magnetic flux having an axial resultant force is producible in the magnet gaps ( 51, 52 ).

The invention concerns a magnetic guiding device having at least oneelement to be guided magnetically in the axial direction, e.g. a shaftor an actuation member that is movable in the axial direction, theelement having a radial flange made of magnetizable material that isenclosed by an axial yoke made of ferromagnetic material andconstituting a stator, forming magnetic gaps in which is producible, bymeans of a combination of permanent magnets and electromagnets, an axialmagnetic flux with which the axial position of the element can beinfluenced.

Magnetic guiding devices are known in many embodiments, and can be usedfor a variety of purposes. One area of application encompasses thesupport of rotating shafts, for example in vacuum pumps, fluidmeasurement devices, blood pumps, gyroscopic devices, or spin rotors. Afurther area of application involves actuators in which a movableactuation member can be moved back and forth in the axial direction bymeans of magnetic force, for example as a pressure plunger, driveelement for small distances, switch, valve actuator, etc. Merely by wayof example, the reader is referred to the following documents from theplurality of publications disclosed for this purpose: U.S. Pat. No.3,976,339; U.S. Pat. No. 5,315,197; U.S. Pat. No. 5,514,924; U.S. Pat.No. 4,620,752; WO 92/15795; U.S. Pat. No. 5,729,065; WO 00/64030; WO00/64031.

FIGS. 3 and 4 of U.S. Pat. No. 5,315,197 and FIGS. 4 and 5 of U.S. Pat.No. 5,514,924 disclose magnetic guiding devices that comprise, as theelement to be guided, a shaft that is magnetically guided in the axialdirection. The shafts have for that purpose a radially projectingannular flange made of magnetizable material that is enclosed on bothsides by an axial yoke made of ferromagnetic material and constituting astator, forming magnet gaps. A radially polarized, permanentlymagnetized annular magnet, which is flanked on each side by a respectiveannular coil of an electromagnet, sits centeredly in the axial yoke. Theresult is to create two magnetic sub-fluxes, located next to one anotherin the axial direction, that combine in the region of the annularmagnet. An axial magnetic flux is generated in the magnet gaps betweenthe annular flange and the axial yoke. By controlling the current in theannular coils, the magnetic flux in the magnet gaps is adjusted in sucha way that the shaft is centered axially in the axial yoke. Deviationsfrom the target position are sensed by a magnetic field sensor that ispart of a controller which controls the current in the annular coils inthe manner described above.

A disadvantage of these known magnetic guiding devices is that as aresult of the radial polarization of the permanent magnet, considerableradial forces are exerted on the shaft and can destabilize the shaft inthe radial direction. The design complexity is moreover considerable,because of the provision of two physically separate electrical coils.

It is the object of the invention to embody a magnetic guiding device ofthe kind cited initially in such a way that instabilities in the radialdirection are avoided as much as possible, and so that the magneticguiding device can be configured substantially more simply in terms ofdesign, and thus more economically.

This object is achieved, according to the present invention, in that inthe axial yoke, at least one pair of axially oppositely polarizedpermanent magnets are arranged axially next to one another, and anelectromagnetic coil is moreover arranged radially adjacently as anelectromagnet, the magnetic flux in the coil being controllable in sucha way that an asymmetrical magnetic flux having an axial resultant forceis producible in the magnet gaps. With the combination of a pair ofaxially oppositely polarized permanent magnets and a radially adjacentlyarranged coil, the provision of two coils can be dispensed with. The onecoil is sufficient to influence the axial magnetic flux in the magnetgaps in the desired manner by appropriate control of the direction andstrength of the current, by the fact that the magnetic field isstrengthened in the one magnet gap and weakened in the other magnet gapas necessary. An axial force can thereby be exerted on the radialflange.

As a result of the particular arrangement of the coil and permanentmagnets, four magnetic sub-fluxes are created in the axial yoke, ofwhich two in each case lie axially, and two radially, next to oneanother. Two of the magnetic sub-fluxes pass through the radial flangeand generate axially and oppositely directed magnetic fields in themagnet gaps. The other two magnetic sub-fluxes pass outward through theaxial yoke. It is understood that multiple permanent magnets and/orcoils can also be provided radially next to one another.

The magnetic guiding device according to the present invention ischaracterized by low instability in the radial direction as well as lessdesign complexity, since only one electrical coil is necessary. Inaddition, the force/current characteristic of the coil is not impairedby the permanent magnet.

If the magnetic guiding device is equipped with a controller, as isevident from the aforementioned documents, the magnetic guiding deviceaccording to the present invention can be used as a magnetic axialbearing for shafts, in which bearing the radial flange is permanentlyaxially centered in a single defined position. The controller thencomprises a magnetic flux sensor that senses axial motions of theelement to be guided (i.e. the shaft) and controls current delivery tothe coil in such a way that the radial flange, and thus the shaft, isheld in substantially stationary fashion in the axial yoke. Additionalradial bearings of mechanical or magnetic type can then ensure radialstabilization.

As already mentioned above, however, such magnetic guiding devices arealso suitable for performing actuations by displacement of the elementto be guided, i.e. for taking on the classic function of an actuator. Acontrol device with which the element to be guided is movable axiallyback and forth out of a defined position is usefully provided for thispurpose. The control device can also be combined with theabove-described control device in such a way that the element is held infloating fashion in the defined position and also during the entirestroke, i.e. the stroke is not limited by stops.

In a further embodiment of the invention, provision is made for theradial flange to be embodied as an annular flange. This embodiment isuseful in particular when the magnetic guiding device serves as an axialbearing for a shaft. The embodiment as an annular flange creates thepossibility of arranging several axial yokes, of the kind describedabove, distributed around the circumference of the annular flange. It issimpler in terms of design, however, to embody the axial yoke as anannular yoke that surrounds the annular flange. The permanent magnetsare usefully embodied in this context as axially magnetized annularmagnets, and the coil as an annular coil.

In order to generate a magnetic field that is as loss-free as possible,the permanent magnets should be in contact in gapless fashion againstthe axial yoke and against one another. For the same reason, the coilshould be in contact in gapless fashion against the axial yoke andagainst the permanent magnets. The only remaining magnet gaps are thusbetween the radial flange and axial yoke.

According to a further feature of the invention, provision is made forthe permanent magnets to be radially adjacent to the circumferentialside of the radial flange, and for the coil to sit radially externallytherefrom. This results in a particularly favorable magnetic flux.

It is understood that the element can comprise several radial flangesone behind another in the axial direction, and each radial flange can beenclosed by an axial yoke having the arrangement according to thepresent invention of permanent magnets and coil.

Provision is further made according to the invention for at least onepreferably magnetic radial bearing additionally to be present for theelement. A radial bearing of this kind (or even several of them) isadvisable particularly when a shaft is to be held in radially centeredfashion, and tilting stresses on that shaft are to be compensated for. Aradial bearing of this kind can also, however, be provided in order toimprove the guidance of an actuation element (actuator).

The magnetic radial bearing should respectively comprise a bearing ringsitting on the shaft and a radial bearing stator axially opposite thatring on at least one side, permanent magnets being provided both in thebearing ring and in the radial bearing stator. Several permanent magnetsshould be arranged next to one another in the radial direction,advantageously being in contact against one another and being polarizedin alternately opposite fashion, i.e. each two adjacent permanentmagnets on the radial bearing stator or on the bearing ring areoppositely polarized. Particularly high magnetic forces are therebygenerated.

It is possible in principle for the radial bearing stators to compriseseveral sub-stators distributed over the circumference and havingpermanent magnets. It is simpler in terms of design, however, to embodythe radial bearing stator as an annular stator and the permanent magnetsas annular magnets.

It is sufficient for each bearing ring to have a radial bearing statorassociated with it only on one side. The radial bearing stator can bearranged and embodied in such a way that an axial force is permanentlygenerated in one direction. This can also occur with an embodiment inwhich the bearing ring is enclosed on both sides by radial bearingstators having permanent magnets. In this way it is possible to achievea particularly powerful magnetic flux that counteracts any radialdeflection of the shaft. It is understood that several radial bearingscan be provided which, in that context, are also differently configured,i.e. the bearing ring of the one radial bearing comprises a radialbearing stator only on one side, whereas the bearing ring of the otherradial bearing has radial bearing stators on both sides. It is alsounderstood that within a radial bearing, several bearing rings having acorresponding number of radial bearing stators can also be provided.This case involves simply a serial arrangement of several radialbearings.

If two radial bearing stators are provided in one radial bearing, theyshould advantageously be combined into one yoke that is U-shaped incross section.

Magnetic bearings have the property that they produce almost no damping.Provision is therefore made according to the invention for at least oneradial bearing stator, preferably all the radial bearing stators, to besupported in radially movable fashion, via spring and damper elements,on a housing-mounted part of the magnetic guiding device. This canoccur, for example, by means of axially extending flexural springs, inwhich context the radial bearing stator can be connected to thehousing-mounted part via several flexural springs distributed over thecircumference. The flexural springs can each be part of a cage thatconnects the ends of the flexural springs via cage rings, and is coupledat one end to the radial bearing stator and at the other end to thehousing-mounted part. To yield a space-saving configuration, the cageshould surround the respectively associated radial bearing stator.

It is additionally useful that the radial bearing stator, suspended onspring elements, is braced via at least one damping element against thehousing-mounted part that damps the radial deflections of the springelements. The damping element can be embodied in each case annularly andcoaxially with respect to the shaft, and can be stressed either incompression or in shear. In a particular embodiment, the damping elementis embodied as a liquid film preferably provided with magnetic ormagnetizable particles, the liquid film being magnetically impinged uponat at least one point via a permanent magnet that can be part of thepassive magnetic bearing. The liquid film is thereby magneticallytrapped. The viscosity of the liquid film can be adapted to theparticular damping requirements.

The invention is illustrated in more detail, with reference to anexemplary embodiment, in the drawings, in which:

FIG. 1 is a side view of a completely magnetic shaft bearing assembly,with a partially sectioned depiction of the upper part;

FIG. 2 is a cross section through a radial bearing of the shaft bearingassembly according to FIG. 1;

FIG. 3 is a perspective depiction of a spring cage for the radialbearing according to FIG. 2;

FIG. 4 is an enlarged depiction of the axial bearing of the shaftbearing assembly according to FIG. 1; and

FIG. 5 shows the axial bearing of FIG. 4 with active influencing of themagnetic flux.

Shaft bearing assembly 1 depicted in FIG. 1 comprises a shaft 2 that issupported in two radial bearings 5, 6 and an axial bearing 9 arrangedtherebetween.

As is evident from the upper part of FIG. 1, shaft 2 is surrounded by atotal of six rings that are axially clamped against a shoulder 10 onshaft 2. A first shaft sleeve 11 having groove 7 is followed by abearing washer 12, a second shaft sleeve 13, a bearing washer 14, athird shaft sleeve 15, and a further bearing washer 16.

Bearing washers 12, 16 belong to radial bearings 5, 6. They arerespectively enclosed on either side by a radial yoke 17, 18 that isU-shaped in cross section and coaxially surrounds shaft 2, each radialyoke 17, 18 comprising a pair of radial bearing stators 19, 20 and 21,22 that form the limbs of radial yokes 17, 18. Radial bearing stators19, 20, 21, 22 and bearing washers 12, 16 comprise permanent magnets 23,24, 25, 26 and 27, 28, 29, 20 that are located respectively opposite oneanother in the axial direction in the two radial bearings 5, 6. They arepolarized in such a way that they attract one another, so that anaxially directed and attractive magnetic force is created in the gapsbetween bearing washers 12, 16 and radial bearing stators 19, 20, 21,22. The magnetic fields center shaft 2.

Permanent magnets 23 through 30 each comprise nine annular magnets(labeled 31 by way of example) set coaxially one inside another, as isevident from the enlarged depiction of radial bearing 6 in FIG. 2. Theannular magnets 31 of a permanent magnet 23 through 30 are in contactagainst one another in the radial direction. Two ring magnets 31adjacent in the radial direction are axially oppositely magnetized. Theaxially oppositely located annular magnets 31 of two adjacent permanentmagnets 23 through 30 are polarized in mutually attractive fashion, sothat an axial magnetic flux results.

Radial yokes 17, 18 are surrounded externally by spring cages 35, 36(omitted in the lower part of FIG. 1) that are connected at the outeredge to radial yokes 17, 18 and at the inner edge to housing washers 37,38 (omitted in the lower part of FIG. 1) that in turn are secured to ahousing 39. Spring cage 36 is depicted individually in FIG. 3. It has atthe edges two cage rings 40, 41 that are connected via eight regularlydistributed spring struts (labeled 42 by way of example) extending inthe axial direction. Spring struts 42 permit a reciprocal paralleldisplacement of the two cage rings 40, 41, in which context springstruts 42 deflect radially. Radial yokes 17, 18 can thus be displacedradially.

Located between radial yokes 17, 18 and housing washers 37, 38 arenarrow gaps in each of which a damping ring 43, 44 is provided (FIG. 1).Damping rings 43, 44 comprise a high-viscosity liquid film containingmagnetic particles. In the context of a radial motion of radial yokes17, 18, the liquid film is stressed in shear and thereby exerts adamping effect. It is trapped in radial yokes 17, 18 by annular magnets45, 46.

Bearing washer 14 belongs to axial bearing 9. It is enclosed on eitherside by an annular yoke made of sheet Si iron. Annular yoke 47 isenclosed and immobilized between the two housing washers 37, 38. It hasan outer yoke shell 48 from which proceed two inwardly directed yokelimbs 49, 50 that have an L-shaped cross section and enclose bearingwasher 14 with limb segments directed toward one another, creating twomagnet gaps 51, 52. Adjacent to the circumferential side of bearingwasher 14 within annular yoke 47 are two permanent magnets 53, 54located axially next to one another which, as symbolized by thetriangles, are polarized axially oppositely. They are in contact againstone another and against yoke limbs 49, 50. They are surrounded by anelectromagnetic annular coil 55 that fills up the space betweenpermanent magnets 53, 54, and between yoke shell 48 and yoke limbs 49,50.

As is evident in particular from FIG. 4, a total of four magneticsub-fluxes 56, 57, 58, 59 are generated by the two permanent magnets 53,54, respectively adjacent magnetic sub-fluxes 56, 57, 58, 59 beingoppositely directed. The inner magnetic sub-fluxes 56, 57 form axiallydirected magnetic fluxes in magnet gaps 51, 52, so that the surfaceslocated opposite one another in magnet gaps 51, 52 attract one another.The magnetic forces cancel one another out in the center position ofbearing washer 14. The outer magnetic sub-fluxes 58, 59 proceed via yokelimbs 49, 50 into yoke shell 48, and from there via annular coil 55 backinto annular magnets 45, 46.

Because of the magnetic instability of shaft 2 in the axial direction,an axial stabilization must be effected via axial bearing 9. Thisoccurs, in the context of an axial deflection of bearing washer 14, bythe fact that this deflection is sensed by a sensor (not depicted herein detail) that is known in the existing art, and as a result thecontroller (likewise not depicted) controls the current delivery toannular coil 55 in such a way that an additional magnetic flux isgenerated, resulting globally in an asymmetrical magnetic fluxdistribution within axial bearing 9. This is evident from FIG. 5. Aminimal deflection of bearing washer 14 to the right exists in thiscase. Annular coil 55 is, as a result, impinged upon by an electriccurrent whose direction is such that the diagonally opposite magneticsub-fluxes 56, 59 are strengthened (symbolized by the more closelypacked flux lines) and the other magnetic sub-fluxes 57, 58 areweakened. As a result, the attractive force in left-side magnet gap 51increases, while the magnetic force in right-side magnet gap 52 weakens.The axial deflection of bearing washer 14 to the right is thus opposedby a magnetic attraction force in the axial direction, with theconsequence that bearing washer 14 is once again centered with respectto annular yoke 47.

Axial bearing 47 depicted in FIGS. 4 and 5 can also be used separatelyfrom shaft bearing assembly 1, for example if shaft 2 is to bemagnetically stabilized only in the axial direction and is supported inthe radial direction by means of plain or rolling bearings. Axialbearing 47 can, furthermore, also be used as an actuator, for example ifshaft 2 is embodied as a plunger. The plunger can, like shaft 2, be heldin a floating position in shaft bearing assembly 1 in entirely magneticfashion. The possibility also exists, however, of supporting the plungerin axially movable fashion by way of mechanical lateral bearing guides.

Within the width of magnet gaps 51, 52, bearing washer 14 (and thereforethe plunger) can be axially displaced by the fact that coil 55 isimpinged upon by a correspondingly directed electric current. The endfaces of yoke limbs 49, 50 can serve as stops in this context. Bycorresponding control of the current acting on coil 55, bearing washer14 can also be axially displaced between two magnetically definedpositions, preventing it from coming to a stop against yoke limbs 49,50. The plunger can be used, for example, to actuate electricalswitches, as a pressure or stamping plunger, etc.

1. A magnetic guiding device (1) having at least one element (2) to beguided magnetically in the axial direction, e.g. a shaft or an actuationmember that is movable in the axial direction, the element (2) having aradial flange (14) made of magnetizable material that is enclosed by anaxial yoke (47) made of ferromagnetic material and constituting astator, forming magnet gaps (51, 52) in which is producible, by means ofa combination of permanent magnets and electromagnets (53, 54, 55), anaxial magnetic flux with which the axial position of the element (2) canbe influenced, wherein in the axial yoke (47), at least one pair ofaxially oppositely polarized permanent magnets (53, 54) are arrangedaxially next to one another, and an electromagnetic coil (55) ismoreover arranged radially adjacently as an electromagnet, the magneticflux in the coil (55) being controllable in such a way that anasymmetrical magnetic flux having an axial resultant force is produciblein the magnet gaps (51, 52).
 2. The magnetic guiding device as definedin claim 1, wherein a controller is present that is embodied such thatthe radial flange (14) is permanently axially centered in the axial yoke(47) in a single defined position.
 3. The magnetic guiding device asdefined in claim 1, wherein a control device is provided with which theelement (2) is movable axially back and forth out of a defined position.4. The magnetic guiding device as defined in claim 1, wherein the radialflange is embodied as an annular flange (14).
 5. The magnetic guidingdevice as defined in claim 4, wherein several axial yokes (47),distributed around the circumference, are provided.
 6. The magneticguiding device as defined in claim 4, wherein the axial yoke is embodiedas an annular yoke (47) that surrounds the annular flange.
 7. Themagnetic guiding device as defined in claim 6, wherein the permanentmagnets (52, 54) are embodied as annular magnets, and the coil (55) asan annular coil.
 8. The magnetic guiding device as defined in claim 1,wherein the permanent magnets (53, 54) are in contact against the axialyoke (47).
 9. The magnetic guiding device as defined in claim 1, whereinthe permanent magnets (53, 54) are in contact against one another. 10.The magnetic guiding device as defined in claim 1, wherein the coil (35)is in contact against the axial yoke (47).
 11. The magnetic guidingdevice as defined in claim 1, wherein the coil (55) is in contactagainst the permanent magnets (53, 54).
 12. The magnetic guiding deviceas defined in claim 1, wherein the permanent magnets (53, 54) areradially adjacent to the circumferential side of the bearing ring (14),and the coil (55) sits radially externally therefrom.
 13. The magneticguiding device as defined in claim 1, wherein the element comprisesseveral radial flanges one behind another in the axial direction, andeach radial flange is enclosed by an axial yoke.
 14. The magneticguiding device as defined in claim 1, wherein at least one radialbearing (5, 6) is additionally present for the element (2).
 15. Themagnetic guiding device as defined in claim 14, wherein the radialbearing (5, 6) comprises a bearing ring (12, 16) sitting on the shaft,and at least one radial bearing stator (19 through 22) axially oppositethat ring on at least one side, permanent magnets (23 through 31) beingprovided both on the bearing rings and on the radial bearing stators (19through 22).
 16. The magnetic guiding device as defined in claim 15,wherein several permanent magnets (23 through 31) are arranged next toone another in the radial direction.
 17. The magnetic guiding device asdefined in claim 16, wherein the permanent magnets (23 through 31) arein contact with one another against the radial bearing stator (19through 22) and the bearing ring in the radial direction.
 18. Themagnetic guiding device as defined in claim 16, wherein in the radialdirection, each two adjacent permanent magnets (19 through 22) areoppositely polarized.
 19. The magnetic guiding device as defined inclaim 15, the radial bearing stator (19 through 22) comprises severalsub-stators distributed over the circumference and having permanentmagnets (23 through 31).
 20. The magnetic guiding device as defined inclaim 15, wherein the radial bearing stator (19 through 22) is embodiedas an annular stator, and the permanent magnets (23 through 31) asannular magnets.
 21. The magnetic guiding device as defined in claim 15,wherein the bearing ring (12, 16) is respectively enclosed on both sidesby radial bearing stators (19 through 22).
 22. The magnetic guidingdevice as defined in claim 21, wherein each two radial bearing stators(19 through 22) are combined into one radial yoke (17, 18) that isU-shaped in cross section.
 23. The magnetic guiding device as defined inclaim 15, wherein at least one radial bearing stator (19 through 22) issupported via spring and damper elements (35, 36; 40 through 44) on ahousing-mounted part (37, 38, 39) of the magnetic guiding device (1).24. The magnetic guiding device as defined in claim 23, wherein thespring elements (35, 36; 40, 41, 42) are embodied as axially extendingflexural springs (42).
 25. The magnetic guiding device as defined inclaim 24, wherein each radial bearing stator (19 through 22) isconnected to the housing-mounted part (37, 38, 39) via several flexuralsprings (42) distributed over the circumference.
 26. The magneticguiding device as defined in claim 25, wherein the flexural springs (42)are each part of a cage (35, 36) that connects the ends of the flexuralsprings (42) via cage rings (40, 41).
 27. The magnetic guiding device asdefined in claim 26, wherein the cage (35, 36) surrounds the respectiveradial bearing stators (19 through 22).
 28. The magnetic guiding deviceas defined in claim 23, wherein the radial bearing stator or stators (19through 22) are braced via at least one damping element (43, 44) againstthe housing-mounted part (37, 38, 39).
 29. The magnetic guiding deviceas defined in claim 28, wherein the damping element (43, 44) is embodiedannularly and coaxially with respect to the element (2).
 30. Themagnetic guiding device as defined in claim 28, wherein the dampingelements (43, 44) are embodied as liquid films.
 31. The magnetic guidingdevice as defined in claim 30, wherein the liquid films (43, 44) containmagnetic or magnetizable particles and are magnetically impinged upon onat least one side via a permanent magnet (45, 46).
 32. The magneticguiding device as defined in claim 31, wherein the permanent magnets(45, 46) are part of the radial bearing or bearings (5, 6).